1. Field of Invention
The present invention relates in general to an optical storage system, and more particularly to an optical storage system using defect signal characteristics to immediately correct a decoding strategy and parameters of a servo controller, and to a method for the optical storage system to control its error correction.
2. Related Art
FIG. 1 is a block diagram showing a conventional optical storage system. As shown in FIG. 1, a conventional optical storage system 10 (such as a CD-ROM drive) includes an optical pick-up head 11, a pre-amplifier 12, a data and timing recovery unit 13, an error correction unit 14, a defect signal generator 15, a servo controller 16, a motor driver 17, and a buffer memory 18. When the optical storage system 10 reads data stored in an optical storage medium, the optical pick-up head 11 first transforms a laser ray reflected by the optical storage medium into an electric signal. Afterwards, the pre-amplifier 12 amplifies the electric signal to generate a radio frequency (RF) signal and a position error signal (such as a tracking error signal or a focus error signal). The defect signal generator 15 generates a defect signal DS according to the RF signal. The data and timing recovery unit 13 generates a modulated signal and a clock signal PLCK according to the RF signal and the defect signal DS. The modulated signal may be EFM, EFM+ or 17PP based on different optical storage media. The error correction unit 14 receives the modulated signal and the clock signal PLCK and corrects errors according to a predetermined decoding strategy so as to output corrected data. The servo controller 16 receives the defect signal DS from the defect signal generator 15 and the position error signal from the pre-amplifier 12 to generate a servo control signal to the motor driver 17. The motor driver 17 controls the move of the optical pick-up head 11. The buffer memory 18 is used for storing data temporarily.
However, when poor quality of electric signals generated by the optical pick-up head 11 occurs as a result of physical defects existing in the optical storage medium itself or other factors, a decoder cannot successfully decode correct information, which in turn leads to a decoding error. Therefore, the conventional optical storage system 10 includes an error correction unit 14 to reduce chances of decoding errors by improving system parameters. In other words, the error correction unit 14 decodes and corrects according to the modulated signal and the clock signal PLCK outputted by the data and timing recovery unit 13 so as to output correct information.
As disclosed by U.S. Pat. No. 7,106,679, a conventional error correction system adjusts the parameters of the servo controller 16, the parameters of a read channel, or the decoding strategy of the decoder to reduce decoding errors after the error correction unit 14 has decoding errors. Nevertheless, this afterwit method only changes the system parameters or the decoding strategy after a decoding error occurs rather than make a corresponding adjustment immediately when a factor likely to cause a decoding error appears.